Issue with Quectel RM520N-GL on Qualcomm QCS-6490 (Yocto) – Unable to Make Calls / Send SMS

Technical Subjects
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1

Hello,
I am using the Quectel RM520N-GL module on a Qualcomm QCS-6490 Yocto image. The module is detected and verified with lsusb, and /dev/ttyUSB* devices are created correctly.

System details:
Linux qcs6490aom2721a1 6.6.52-yl01301-ga97804e47e26 #1 SMP PREEMPT Wed Apr 2 14:43:28 UTC 2025 aarch64 aarch64 aarch64 GNU/Linux

lsusb output:

Bus 003 Device 003: ID 2c7c:0801 Quectel Wireless Solutions Co., Ltd. RM520N-GL
Bus 003 Device 002: ID 05e3:0625 Genesys Logic, Inc. USB3.2 Hub
Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 05e3:0610 Genesys Logic, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Created devices:
root@qcs6490aom2721a1:~# ls /dev/ttyUSB*
/dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyUSB2 /dev/ttyUSB3

WWAN interface:
wwan0 Link encap:Ethernet HWaddr EA:A9:EA:93:58:3C
inet addr:169.254.190.247 Bcast:169.254.255.255 Mask:255.255.0.0
inet6 addr: fe80::b7ba:edf0:6176:dd98/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

AT command tests (via /dev/ttyUSB2):

microcom -s 115200 /dev/ttyUSB2
AATT

OK
ATD+9173XXXXXXXX;
ATD+9173XXXXXXXX;
NO CARRIER

AT+QCFG=“ims”
AT+QCFG=“ims”
+QCFG: “ims”,0,0

OK

AT+CMGF=1
AT+CMGF=1
OK
AT+CMGS=“+9173XXXXXXX”
AT+CMGS=“+9173XXXXXXX”

HHeelllloo ffrroomm QQuueecctteell
+CMS ERROR: 350

AT+CREG?
AT+CREG?
+CREG: 0,0

OK
AT+CGREG?
AT+CGREG?
+CGREG: 0,0

OK
AT+COPS?
AT+COPS?
+COPS: 0

OK
AT+CPIN?AT+CPIN?

+CPIN: READY

OK
AT+CSQ
AT+CSQ
+CSQ: 14,99

OK
AT+QCFG=“nwscanmode”,0,1AT+QCFG=“nwscanmode”,0,1

ERROR
AT+QCFG=“?”
AT+QCFG=“?”
ERROR

Issue:

While trying to make a call or send an SMS, I get errors (NO CARRIER or +CMS ERROR: 350).
The SIM is detected (+CPIN: READY), but registration fails (+CREG: 0,0 and +CGREG: 0,0).

Could anyone guide me on how to proceed further with network registration and resolving this issue?
Thanks in advance!

2

It is not registerred in LTE or NR at all.

3

Hi Wang

Thanks for the reply. I understand that +CGREG: 0,0 means the module is not registered on LTE/NR.

I tried running the following command to force LTE/NR:

AT+QCFG=“nwscanmode”,3,1

But I am not getting any response (not even OK or ERROR).

Could this be related to firmware version or SIM/operator compatibility?
Are there other AT commands I should use to troubleshoot why the module is not registering on LTE/NR

Extra info:
SIM is detected: +CPIN: READY
Signal is available: +CSQ: 14,99
But registration fails: +CREG: 0,0, +CGREG: 0,0
Any guidance on the correct scan mode settings or next steps for registration would be really helpful.

Thanks in advance!

4

I am not sure whether you have locked the mode or the band.
Or it is just the problem of the SIM card.

5

AT+QNWPREFCFG=“mode_pref”
AT+QENG=“servingcell”

6

AT+QNWPREFCFG=“mode_pref”
ERROR

AT+QENG=“servingcell”
ERROR

7

image
image1053×558 166 KB

8

Hi Wang,
Thank you for your quick support. I tried using the echo command and got the following response:
It seems the modem is trying to connect to the network but cannot.

Could you advise what I should do next?

The SIM is inserted but not yet registered on the network. Do I need to register the SIM with the network manually?

The signal appears to be very weak, or there’s no coverage. I am not connected to the antenna—could that be causing the issue?
Here are the commands I ran and their outputs:

root@qcs6490aom2721a1:~#echo -e ‘AT+QNWPREFCFG=“mode_pref”\r’ > /dev/ttyUSB2
root@qcs6490aom2721a1:~# cat /dev/ttyUSB2
AT+QNWPREFCFG=“mode_pref”
+QNWPREFCFG: “mode_pref”,AUTO

OK

^C
root@qcs6490aom2721a1:~# echo -e ‘AT+QENG=“servingcell”\r’ > /dev/ttyUSB2
root@qcs6490aom2721a1:~# cat /dev/ttyUSB2
AT+QENG=“servingcell”
+QENG: “servingcell”,“SEARCH”

OK
I would appreciate any guidance on the next steps.
Thanks in advance!

9

Can you try another SIM card?
+QENG: “servingcell”,“SEARCH” means that it is still searching and not registerred.
Are the four antenna connected?